1. Field of the Disclosure
This invention relates to a method of manufacturing a composite material. In particular, the invention relates to a method of manufacturing a composite material including at least one reinforcing element.
2. Description of the Related Art
Laminated composite materials, in which reinforcing fibres are held within a polymeric matrix, are extensively used in many engineering applications. Such materials can generally provide a higher strength and stiffness per unit weight than conventional metallic materials. This makes such composite materials advantageous for weight sensitive applications, such as those in the field of aerospace.
A known problem with laminated composite materials is their poor inter-laminar, or through-thickness, mechanical properties in comparison to the corresponding in-plane properties. Such low inter-laminar strength and fracture toughness can constrain the design of composite parts and may even limit the use of such materials for certain applications.
One solution to this problem is the use of a toughened matrix material. Such matrix materials are generally significantly more expensive than conventional matrix materials, often have poor high temperature properties and may still not provide a sufficient increase in fracture toughness.
An alternative solution to improving inter-laminar strength properties is the insertion of through-thickness fibres into the laminated material. Various techniques have been developed for the insertion of such reinforcing fibres.
One method for inserting through-thickness reinforcing fibres into the laminated material is stapling or z-pinning. These reinforcing fibres are generally fibrous in structure and may be formed with a 45° chamfer at the insertion end.
Through-thickness reinforcing fibres are intended to resist shear forces so as to improve the inter-laminar strength and fracture toughness. Without the presence of the through-thickness reinforcing fibres the composite may de-laminate when exposed to shear forces.
Although the presence of the through-thickness reinforcing fibres increases the intra-laminar strength of the composite material, their presence in the structure can introduce an altogether different weakness. Due to the shear forces to which they are subjected, the through-thickness reinforcing fibres can act as a crack initiation point in the laminated structure. From the insertion point in the composite material, such cracks tend to form in a direction perpendicular to the through-thickness direction of the reinforcing fibres.
The only known solution to this problem is to provide a larger number of reinforcing fibres for a given area or volume of composite material. Naturally, this increases the time and cost of manufacturing the composite material and, by extension, the resulting completed component. Furthermore, in itself this solution does not prevent cracks forming around the reinforcing fibres.
A further problem with the conventional z-pinning process is that the fibrous reinforcing pins can split or fracture during insertion as a result of the need to force the pins through the densely compacted fibre layers of the laminate and/or through the resin (for example where the fibres are pre-impregnated with resin). This can reduce the effectiveness of the presence of the reinforcing pins.